2D kernel-based imaging of coda-Q space variations in the Gargano Promontory (Southern Italy)

Abstract

Crustal seismic attenuation in the Gargano Promontory (Southern Italy) was inferred by analyzing coda waves of about one hundred small magnitude earthquakes recorded by the OTRIONS local seismic network. Coda attenuation Qc was computed using the Sato (1977) model, i.e. the assumption of single back-scattering, at different lapse times and at different frequencies. Average Qc is comparable with the same quantity measured in the adjacent area of the Umbria–Marche region (central Italy). A recent kernel-based imaging technique for Qc was then applied and the results evidence a well confined zone located South West of the investigated area, showing a sharp Qc anomaly. While Qc cannot be directly related to the physical properties of the propagation medium, its spatially-dependent modeling allows an interpretation in the light of other geophysical and geological information. Our results were then interpreted following the two extreme hypotheses according to which Qc could be representative of the effect of only intrinsic attenuation or of only scattering from the heterogeneities. Both the hypothesis correlate with the observation of anomalies in several geophysical parameters, such as heat flow, magnetic field, gravity, density, seismic velocity in the southwestern Gargano. Moreover, the Qc images support the results obtained in a recent study that shows clear variations in the rheological properties of the Gargano. The results obtained at local scale confirm and detail previous regional scale studies on attenuation and highlight for the first time the presence of a positive Qc anomaly in the south-western part of the Gargano Promontory.